Re: [Xen-devel][Patch] MTRR virtualization

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 19 Jun 2006, at 09:29, Dong, Eddie wrote:

> For example, a guest may set video frame buffer to be "WC". But in Xen
> environment, as we are using memory (RAM) to back for guest video 
> frame,
> we have to set the memory type to be "WB" otherewise the access using
> aliase address in Qemu (WB attribute) may cause mca.
> Current shadow simply copy guest PAT entry to shadow PTE even for video
> frame buffer, this works as if the guest is setting PAT as "WB" and 
> MTRR
> as "WC".
> On the otherhand, if guest is setting PAT as "WC", and MTRR as "WB", we
> have
> problem. Because in this case, shadow PAT="WC", machine MTRR = "WB",
> and thus we get "WC" for this video frame. MCA may happen.
The correct approach right now is to set WB for everything. HVM guests 
currently never directly map I/O resources. Anything more complicated 
than that, until we actually support direct I/O access, is quite mad.
 -- Keir


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel